To start the Reaper missions you have to get the Heck Butterfly and the Swallowtail Butterfly from D-rank Missions, and you have to get the Blue Flower Hairpin by winning three Hairpin Pieces from the party house and then completing a special mission.
I've gotten the Heck Butterfly and one Hairpin Piece, so I've still got a ways to go.
By the way Artanis, are you willing to spar with me? I asked you in the village menu but you never answered.
Be the Ultimate Ninja! Play
Billy Vs. SNAKEMAN today!